This is the point where for a 'normal' game (like Fishy Business) I would be thinking about trying to get it published. However being a microgame, I'm not sure that is really practical. I don't think established games publishers are going to be interested, because basically it's impossible to make any money out of publishing and selling such a small and cheap thing. This article by Michael Mindes, who knows a thing or two about making money from games and otherwise, explains the problems.
(There is of course the option of self-publishing, but really I'm too busy to take on all the work required in sorting out manufacture, finding distribution, marketing and selling.)
T suggested coming up with two further microgames each using 18 cards, so they could all be printed and packed together as a set ina conventional pack-of-cards-sized box. That is quite appealing as a designer (particualrly as Shape Up! only took three months from initial conception to reach this point) but I'm still not sure a publisher would really be keen.
So I guess I might end up just giving it away as a print-and-play PDF. Which would still be very cool if lots of people did so, but it does seem a bit of a shame when the properly-printed cards are so nice to look at and handle.
Anyway, this is all very much first-world problems; the main thing is that people have been playing Shape Up! and liking it! Which makes me very happy.